TiN thin coating is deposited on the surface of 3Cr13 stainless steel by multi-arc ion coating technology. The effects of large particles, nitrogen flow rate and target current on the color properties of the films were investigated by scanning electron microscopy and visible spectrum photometer. The results show that the large particles consist of surface crystal layer, intermediate layer, and droplet layer, and less quantity of large particles does not affect the color performance of the film. When increasing the nitrogen flow rate, the reflectance of the sample showed a downward trend, the color coordinates red/green value a* and yellow/blue value b* increased, the lightness L* decreased, the chroma index C*ab increased, and the hue angle H*ab decreased, the film color gradually changed from silver gray to dark yellow. However, as the target current increased, the hue angle H*ab increased, the chroma index C*ab, the red/green values a*, and the yellow/blue values b* all decreased, the film color gradually changed from deep yellow to silver white. The change of the target current changes the atomic ratio of titanium, and it can compensate for the change of nitrogen flow.
Stainless steel itself has excellent corrosion resistance, wear-resistance and other characteristics, has now it has been widely used in daily life, automotive industry, construction and other areas, with the expansion of its demand areas, colored stainless steel quietly come out. The colored stainless steel not only increases the decorative and artistic properties, but also improves the corrosion resistance and wear resistance of the steel. Today, the application of color stainless steel is becoming more and more extensive and the requirements are getting higher and higher. The surface treatment technology of stainless steel directly affects the application and development of color stainless steel, and it also has great practical value and practical significance for the study of stainless steel surface coloring.
TiN film has the advantages of high hardness, good chemical inertness, unique color, etc. It is widely used in wear-resistant and corrosion-resistant surface coatings, semiconductor diffusion barriers, and decoration industries. The use of multi-arc ion plating technology to make gold-imitation titanium nitride decorative film on the metal surface has the advantages of high production efficiency, low process cost, stable film performance, etc. This method has already entered the practical production stage. The purpose of this paper is to systematically study the influence of large particles, nitrogen flow and target current on the color of the TiN films as well as the change rules, to provide the basis for the making of titanium nitride imitation gold decorative film by multi-arc ion coating technology and the optimization of the color of the film.
1. The experimental Content
1. 1. Experimental equipment and materials
In this experiment, AIP-01 type multi-arc ion coating machine was used for coating. The sputtering target was a titanium target with a purity of 99.9%. The working gas was argon gas (Ar) with a purity of 99. 99%. The reaction gas was nitrogen (N2) with a purity of 99.99%, the substrate is 3Cr13 stainless steel with dimensions of 40 mm × 20 mm × 2 mm.
1. 2. Experimental method
After grinding and polishing, the substrate was ultrasonically washed with acetone and absolute ethanol for 15 min in sequence, and then placed it in a coating machine after drying. Then pumping vacuum to the degree of at least 6.0×10-3 Pa, and heating to the deposition temperature. Argon gas was aerated to work pressure, then start the arc target first to coating a pure titanium bottom layer in 5min (process is shown in Table 1), and then aerate the nitrogen to deposit a TiN film.
Table 1 Pure titanium plating process
|Ti Target Current/A||Ar Flow /L/min||Vacuum Degree/Pa||Bias/V||Tempearture/℃|
The surface of the sample was coated with different process parameters (nitrogen flux and target current), and then using LEO-1530VP field emission scanning electron microscope (FE-SEM) to observe the morphology of the film.
The color properties of TiN films were measured by a Perkin Elmer Lambda 950 UV/Vis spectrophotometer. Referred to three types of illuminants recommended by the International Commission on Illumination (CIE): Standard illuminants A, C, and D65. The spectral reflectance ρ(λ) of the film is measured by spectrophotometer, and then used its own data analysis system to calculate the three orthogonal parameters of the LAB color coordinates under the three standard illuminants: L*, a*, b*, in the national standard CIE 1976 (L*, a*, b*) color system, L * indicates the brightness of the color (L* = 0 generates black and L* = 100 indicates white), a* indicates red-green direction (+a* indicates red direction, -a* indicates green direction), and b* indicates yellow-blue color direction (+ b* indicates yellow direction, - b* indicates blue direction). The color coordinates h*ab and the chroma index C*ab are calculated by the color coordinates. The hue angle H*ab represents the dominant wavelength, and the chroma index C*ab represents the color purity:
H*ab=arctan (b*/a*) (1)
(1) Most large particles consist of droplet layer, intermediate layer and crystalline layer. The crystalline layer is exposed on the surface. When the number of large particles is small, the influence on the color of the film is small. If the number of large particles is too large, the large particles covering the film, the reflectance and the brightness of the film will decrease.
(2) Titanium nitride films that color ranging from silver to dark yellow can be made under different nitrogen flow conditions. As the nitrogen flow rate increases, the film reflectivity curve decreases, showing decrease in brightness L* and hue angle H*ab, and increase in red/green value a*, a yellow/blue value b*, and a saturation index C *ab in the LAB chromaticity space.
(3) As the target current increases, a titanium nitride films that color ranging from deep yellow to silver white can be made, exhibiting increase in the hue angle H*ab and color index C*ab, and decrease of the red/green value a* and the yellow/blue value b* in the LAB color space. As the change of the target current can change the atomic ratio of titanium and nitrogen in the film, to compensate the change of the nitrogen flow rate. Therefore, the degree of The L* gradually increases in the front part as the target current increases, and the decrease of the L* value in the rear part should be caused by generation of a large number of large particles and other defects in the film layer as the current further increases.